In computer systems, a pointing device is an apparatus by which a user performs an action to navigate focus to particular points on a screen of a display, usually indicated by a cursor. The most common type of pointing device is the so called mouse, which is ubiquitous as a peripheral device in the personal computer environment. Early mouse versions use a track ball, together with X and Y encoders which are rotated by motion of the track ball as it is rolled along a surface. The encoder values are then transformed into electrical signals and processed by a computer to represent an on-screen position of a cursor. Various actions can be carried out either by functional buttons provided on the mouse body, or by other peripheral devices such as keys of a computer keyboard for example. The actions taken will depend upon where the cursor is focused.
It is also known to provide optical mice, which comprise a radiation source and an image sensor. The radiation source emits radiation upon a surface and the image sensor is arranged to receive light reflected from the surface. Movement of the mouse is detected by determining the difference in the images in the X and Y directions as the mouse is moved along a surface. The radiation source typically comprises a light emitting diode (LED) that emits light in the infra-red or near infra-red spectra.
Many other types of pointing devices are known, such as track balls, touch screens, and joysticks.
One common type of pointing device is a touch pad. These are commonly provided with laptops, although they can also be provided as a stand alone device. A touch pad typically functions by measuring the change in capacitance between conductor layers that occurs when a user's finger is placed on the pad. An array of conductors is provided, so that the location of the point of incidence can be determined. The motion of the finger across the pad can therefore be used to move an on-screen cursor in a manner similar to the detected motion.
Capacitance based touch pads are also found on a variety of mobile devices. Various mobile phones and personal digital assistants (PDA's) include so called “finger mouse” touch pads, essentially being a miniature version of the touch pads normally found on laptop computers.
Other portable devices such as dedicated MP3 players comprise touch pads for scrolling through lists. For example, the popular Apple® iPoD® MP3 player comprises a capacitive scroll wheel touch pad. This is an example of a touch pad of the type comprising a closed path, which can be repeatedly navigated around by a user when scrolling through a list. Different directions of navigation along the path (for example, clockwise or anti-clockwise around a circle) give different directions of navigation along a list (up or down, in the case of a normal list, or in similar clockwise or anticlockwise directions in the case of a list or menu that has a three dimensional display effect).
A major problem is however encountered with capacitive type touch pads. They do not work in situations where a virtual connection to ground is not provided, for example if a user is wearing a glove or uses a stylus to operate the device.
It is also known to provide touch pads that use similar technology to PC based optical mice, employing image processing technology which identifies features in the image and tracks them between successive frames to determine the motion of a user's finger over a mousing surface. These “optical” touch pads can be found on some mobile devices, for example the BlackBerry® Curve 8520 mobile telephone. An optical touch pad can be referred to as a finger mouse.
An optical touch pad can be operated with a stylus or with gloved fingers, however existing designs cannot cope well with designs that involve movement in a circular motion or around some other closed path, as the user model for a personal computer is based on the assumption that most operations require either horizontal movement or vertical movement, and occasionally diagonal movement. In addition, due to the limited sensing area of existing optical touch pads with respect to the size of the human finger, it is even more difficult to perform tasks based upon movement of a finger in a circular motion or around some other closed path without having to move the finger away from the sensing area. Moving away from the sensing area requires repositioning over the mousing area for a second or further pass which creates a less enjoyable user experience and can often result in inaccurate movement.
It is therefore desirable to provide a touch pad that does not rely on capacitive methods, but that is robust for dealing with motion of a user's finger along a closed path circuit, including for example a circle or similar.